sometimes we can end up with two hosts with the same hostname. this is bad (see
ZBX-6828 and other issues).
suggested remedy - try to detect this happening when reloading configuration cache. if it is detected, print a warning in the logfile (but continue working).
warning should include : hostname and host ids.
this warning should be printed also when obtaining information for a proxy - if there are two hosts with the same name on that proxy